The present study develops a protocol for rapid in vitro micropropagation of a critically endangered and floriculturally most important epiphytic orchid, Dendrobium primulinum Lindl. through the culture of small shoot tip explants (0.3 to 0.5mm) derived from in vitro grown seedlings. The shoot tip explants cultured on solidified Murashige and Skoog (MS) basal medium and MS medium alone or supplemented with combination of various concentrations of growth regulators; α-naphthalene acetic acid (NAA) and 6-benzylaminopurine (BAP), produced shoots and multiple shoots. The maximum numbers of rootless healthy shoots were observed on MS medium fortified with BAP 1.5 mgl-1 with an average value of 4.5 shoots per culture where shoot multiplication was initiated after 5 weeks of culture of shoot tip. Among the different tested combination, MS medium with BAP (1.5 mg l-1) and NAA (0.5 mg l-1) were most effective for the shoot multiplication. MS medium supplemented with various concentrations of rooting hormones viz. NAA, IAA and IBA showed positive response in development of roots, except NAA 0.5 mgl-1. The rooting was observed after 3 weeks of culture of shoot tip. The various concentrations of IAA and IBA were found to be effective hormone for rooting of D. primulinum in comparison to NAA. The best rooting response was observed on MS medium with exogenous supply of IAA 0.5 mgl-1. The well developed in vitro rooted plantlets were hardened successfully in the potting mixture containing cocopeat and sphagnum moss in the ratio of 2:1. Nearly 70% of plantlets survived.
